HYDRAULICS OF DUCKBILL ELASTOMER CHECK VALVES

Duckbill-shaped elastomer check valves are sometimes installed on stor m-water or sewage outfall ports to prevent backflow or seawater intrus ion. Unlike fixed diameter ports, the jet velocity varies nonlinearly with port discharge flow an analysis of all available experimental dat a on the head-discharge characteristics of check valves shows that the collective data can be effectively correlated with the parameters of the approach flow in the discharge port, Two dimensionless relations a re obtained for the effective percentage jet opening area and the valv e head loss. The relations are derived from data for nominal port diam eters in the range of 100-305 mm (4-12 in.), and appear to hold genera lly for elastomer check valves. The head-discharge relations can be us ed to determine the jet discharge velocity and opening area that are n eeded as input to numerical plume models for environmental impact asse ssment and outfall design. The results can also be conveniently incorp orated into a diffuser hydraulics code. In general, the calculations s how that the use of duckbill check valves leads to a more uniform port discharge distribution, higher jet velocities, and higher energy head requirements.